This invention relates to the removal of sulphur compounds from stack and other vent gases, then wet oxidizing the sulphur compounds into product acids.
In recent times considerable public interest has been focused on pollution of the atmosphere as a result of burning fuels. In the industrial sector particular attention has been directed to the emissions from smoke stacks, which in the United States has resulted in federal requirements limiting certain contaminants. From an industrial point of view perhaps the most troublesome limitation is a maximum allowance of 1.2 lb. of SO.sub.2 to be emitted in the stack gas for each million BTUs fired. Such limitation in effect establishes the maximum sulphur content of the fuel to be burned unless sulphur removal methods are employed.
Among the fuels, coal particularly is affected because much of the coal available contains too much sulphur to meet the standards. One solution is to use low sulphur coal. Another is to blend low sulphur coal with high sulphur coal in such proportions as to remain within standards. Another solution is to remove the sulphur from the coal before burning, a process at the present state of the art that is generally too costly for serious consideration.
Still another solution, which is gaining favor in recent times, is to remove sulphur compounds from the stack gas (sometimes called flue gas). Removing sulphur compounds generally falls into two categories: residue disposal systems and regenerable systems. Among the better of the residue disposal systems are those that use a slurry of limestone or lime to absorb SO.sub.2, resulting in an end-product sludge that, unfortunately, has no commercial value. Among the regenerable systems one of the better processes absorbs SO.sub.2 in a solution of sodium sulphite which then is converted into bisulphite. After several other processing steps, SO.sub.2 is segregated in concentrated form for further conversion downstream into elemental sulphur or sulphuric acid. In the coarse of the process sodium sulphite is regenerated and recycled. With the trend toward regenerable processes of sulphur removal, in spite of the fact that the best of the systems use about 3% of the output from an electric generating plant, it appears obvious that a significant improvement is needed to reduce the operating costs attributable to the scrubber system. The present invention is designed to simplify the steps and reduce the energy required for scrubber system operation.
Other vent gases or atmospheric discharges that can be treated with the methods of the present invention are sour gas wells, refineries, and manufacturing process plants using sulphur bearing compounds in their processes.
It is an object of the present invention to teach methods of sulphur removal from stack gases wherein an inert scrubber liquid is used to absorb the sulphur compounds. It is another object of the present invention to teach the removal of the sulphur compounds from the inert scrubber liquid by wet oxidation of the sulphur compounds into product acid. Other objects, capabilities and advantages of the present invention will become apparent as the description proceeds and upon reference to the drawing.